Windmills have been known for decades and perhaps centuries. Windmills were used to an appreciable extent, particularly on farms, during the early part of this century. Their use declined during the middle of this century as low cost energy from fossil fuels became increasingly available. Within the last decade or so, sharply rising costs of fossil fuels, coupled with the realization that supply of fossil fuels is not inexhaustable, has once again led to an interest in windmills. Even so, wind driven devices today produce only a very small fraction of the world's energy needs. This is no doubt due in large part to deficiencies in wind driven energy producing devices currently available.
U.S. Pat. No. 4,204,795 to Forrest describes a device for transforming wind energy into rotary motion, or a windmill which comprises a plurality of semi-cylindrical wind collecting blades circumferentially spaced about a horizontal shaft. The device is placed in a pit dug in the earth's surface, and mounds of earth are piled up on either side to serve as deflectors for directing the wind only against the upper portion of the apparatus. A generally similar apparatus is shown in U.S. Pat. No. 4,357,130, also to Forrest.
U.S. Pat. No. 4,269,563 to Sharak et al, shows a wind turbine or windmill comprising a vertical rotating shaft, a rotar having a large number of circumferentially spaced semi-circular wind collectors, and air guides to direct air against the collectors and thereby improve efficiency of the device.
The Forrest devices apparently require a horizontal shaft, a pit and mounds of earth on either side for most efficient operation. The considerable earth moving required adds tremendously to the cost of installing such device. This in turn greatly limits the usefulness of these devices.
The Sharak et al device requires air guides for most efficient operation. While the cost of providing air guides does not approach the cost of earth moving as required in the Forrest devices, nevertheless such air guides do add appreciable to the cost of the windmill.